Polymers in the form of small spherical particles are useful for many industrial applications such as for easy metering and filling of molds and extruders, for the manufacture of ion exchangers, sorbents, molecular sieves, carriers of catalysts etc. Small spheres or beads of polymers are usually made by polymerization or copolymerization in suspension. This method cannot be used, however, in the case of ready-made or natural polymers and their derivatives.
Suspension polymerization has, in cases where it can be used at all, several inconveniences. The size of the particles increases with increasing degree of polymerization and is not easily controllable. At high conversions the viscosity rises so that the particles become sticky, agglomerate and separate from the dispersing medium. Therefore "stabilizers" of suspension are often added, contaminating the product and raising the production cost. When manufacturing copolymers, neither any of the monomers nor the copolymer must be soluble in the dispersing medium: This condition cannot be always easily realized, having regard to the different characteristics of the monomers. This problem is further complicated if various additives are to be used such as dyestuffs, foaming agents or biologically active substances. Another disadvantage of suspension polymerization is its long duration and high energy requirement.
It is known e.g. from the U.S. Patent Specification No. 3,597,350 (Determann et al) to prepare cellulose in spherical form by dispersing viscose in an organic solvent, adding a detergent, and also adding an acid which is soluble in the dispersing phase. A suitable acid is e.g. benzonic acid. Alternatively the viscose suspension is poured into a solution of benzoic acid. in benzene. In this case, the coagulating agent is dissolved in a solvent miscible with the dispersing medium and the coagulation is a chemical process - decomposition of cellulose xanthogenate.
According to another method a suspension of viscose in a mineral oil is gelled by heating, and regeneration of cellulose in bead form is carried out by adding an oil-soluble acid, preferably acetic acid. (Peska et al, Czechoslovak Pat. Appln. No. PV 3858-74).
Still another method of preparing spherical particles from film waste from cellulose acetate or acetobutyrate consists of suspending solutions of said waste in organic volatile solvents immiscible with water in an aqueous solution of an emulsifier. The aqueous solution is heated to the boiling point of the organic solvent which is distilled off. Here the coagulation is brought about by removing the solvent preventing the polymer from contact with water in which the polymer is not soluble. (Czechoslovak Pat. No. 109217, Sramek et al). This method is requires considerable energy and is time concuming; It cannot be used generally.